The present invention relates broadly to antenna structures, and in particular to a deployable folded antenna apparatus.
There are several different types of antenna structures that are used in communication and navigation systems. While each type is unique in its application, paraboloidal-type antennas have been found to be particularly useful in many of such systems. However, the use of paraboloidal antennas is normally limited because of the reflector size, the surface and contour tolerance that can be maintained when using higher frequencies and their weight. Thus while in many applications it is particularly advantageous to use large paraboloidal reflectors, it is often necessary to build up the structure in rather inaccessible or inconvenient places which makes their use impractical in these inaccessible places. As for example, it is difficult to use a parabolic reflector antenna of large size in space, because of the difficulty of lifting such a large structure into space and assembling it there. Further, it is usually impractical to use large paraboloidal antennas on, for example, small ships or the like where space is limited. Thus, in many such applications smaller paraboloidal antennas are used when larger ones are desired.
There are several expandable antenna structures that have been used in attempts to solve the foregoing problems. Examples of these antenna structures are assembled rigid panelled modules, hinged rigid panels, and inflatable structures. Such structures are either constructed or expanded at point of use into the large paraboloidal reflector. In using such structures, it is necessary that the imperfections in the structure be held at a minimum since as the wavelength becomes shorter, the imperfections in the structure become an appreciable fraction of the wavelength. In this regard, the rigidity of inflatable-type structures is difficult to maintain. Modular-type construction and hinged rigid panels are limited in use by their heavy weight and because they are difficult to assemble at point of use, and because it is difficult to package them compactly. It would therefore be advantageous to have a relatively lightweight, expandable paraboloidal antenna that is easily and automatically expanded into a paraboloidal reflector at point of use and which paraboloidal antenna, when expanded, has a rigid truss-type structure that assures a contour tolerance that will permit the transmitting or receiving of higher frequency signals.